JPH04533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a motor control device that detects the rotational position of a brushless motor using light.

[Prior Art] An optical displacement converter projects light onto transparent slits formed at a predetermined pitch on a code plate, detects the light passing through the transparent slits with a light receiving element, and detects the detected light. The displacement of the code plate is determined based on the .

Conventionally, such displacement transducers include, for example,
Japanese Patent Application No. 13951/1983 (Japanese Unexamined Patent Publication No. 59/1989) filed by the present applicant
138921) was a "displacement converter".

In this displacement converter, the angular resolution is determined by (number of transparent slits) x (number of interpolations per pitch of transparent slits). For example, the number of slits is 160 and the number of interpolations is
In the case of 4096, the angular resolution is 360/655360 degrees.

[Problems to be Solved by the Invention] When this displacement transducer is used in a brushless DD motor (Direct Drive Motor), it can be used not only as a simple displacement transducer, but also as a transducer for the teeth provided on the rotor and stator of the DD motor. It is also used to detect the position of the motor and provide a signal that is the basis of control (hereinafter referred to as commutation control) to flow two-phase, three-phase, etc. excitation current to the motor coil. For this reason, it has conventionally been necessary to make the number of light-transmitting slits in the motor equal to the number of teeth in the motor.

Therefore, the following problems arose.

Since the number of slits in the code plate cannot be increased,
Accuracy is poor.

Since the pitch of the slits becomes larger, a larger light source is required.

Since the radius of the slit formation position cannot be made large, the hole in the center of the code plate cannot be made large, making it difficult to pass the wiring for the motor and displacement transducer.

The present invention was made to solve the above-mentioned problems, and uses an optical displacement converter to
It is an object of the present invention to realize a motor control device capable of commutation control by increasing the number of light-transmitting slits than the number of teeth of the motor.

[Means for Solving the Problems] The present invention includes: attaching a code plate on which transparent slits are formed at a predetermined pitch to the rotor of a brushless motor; projecting light onto the transparent slits; In a motor control device that determines the positional relationship between teeth of a rotor and a stator of the motor based on passing light, the code plate is provided with a two-stage slit row with the number of light-transmitting slits n ₁ and n ₂ , n ₁ − _{n 2} (n ₁ > n ₂ ) is set to the number of teeth of the motor, and is determined from the phase difference between the detection signals of the light that has passed through the n ₁ and n ₂ transparent slits. A motor control device characterized in that it includes a signal processing unit that determines the positional deviation of teeth of a stator.

[Example] Hereinafter, the present invention will be explained using the drawings.

FIG. 1 is a block diagram of an embodiment of a motor control device according to the present invention.

In the figure, reference numeral 1 denotes a disc-shaped code plate, and two rows of light-transmitting slits are provided in which light-transmitting slits are arranged at predetermined pitches in the circumferential direction. The outer slit row is provided with _n1 light-transmitting slits 2, and the inner light-transmitting slit row is provided with _n2 light-transmitting slits 3. These translucent slits 2 and 3 are provided to detect misalignment between the teeth of the motor's rotor and stator. A slit S is provided outside the slit 2 as a slit for detecting the rotational position of the code plate 1. This code plate 1 rotates together with the output shaft M of the motor.

4 and 5 are light sources, and 6 and 7 are lenses for converting the light beams from the light sources 4 and 5 into parallel beams.

The light that has passed through lens 6 hits slits 2 and S, and the light that has passed through lens 7 hits slit 3.

8, D ₁ , and D ₂ are image sensors that receive the light (slit image) passing through the light-transmitting slit 2 .
The photodiode array 8 is, for example, eight photodiodes 8 ₁ to 8 ₈ arranged in an array.

9 is an image sensor that receives the light (slit image) that has passed through the transparent slit 3;
photodiodes 9 ₁ to 9 ₈ are arranged in an array.

These photodiodes are arranged within one pitch P of the light-transmitting slit, as shown in FIG.

10 is a signal processing section, and a photodiode 8
The positional relationship between the rotor and stator teeth of the motor is calculated based on the detection signals ₁ to ₈₈ and ₉₁ to ₉₈ .

A specific example of the configuration of such a control device is shown in FIG. Components in FIG. 3 that are the same as those in FIG. 1 are given the same reference numerals. The same applies to the figures below.

In FIG. 3, SW1 to SW8 are switches that sequentially take out signals from photodiodes 8 ₁ to 8 ₈ and 9 ₁ to 9 ₈ at a fixed timing.

11 and 12 are OP amplifiers, and each switch
Amplify the signals applied via SW1 to SW8. The outputs of the OP amplifiers 11 and 12 have a stepped waveform. The height of the waveform corresponds to the number of photodiodes that detected light.

13 and 14 are low-pass filters, which extract signal components in the low frequency range of the OP amplifiers 11 and 12. The outputs of the OP amplifiers 11 and 12 become periodic function waveforms by passing through the low-pass filters 13 and 14.

Comparators 15 and 16 shape the waveforms of the signals f ₁ (t) and f ₂ (t) from the low-pass filters 13 and 14.

17 is a phase difference counter, and a counting clock
Signals f ₁ (t) and f ₂ (t) based on the timing of CLK
Count the phase difference. The signal f ₁ (t) is used to reset the counter value, and the signal f ₂ (t) is used to strobe the counter value. If you want to divide one period of these signals by 1024, use the coefficient clock.
CLK frequency f _c is 1024 f _s (f _s is signal f ₁ (t), f ₂ (t)
frequency).

18 is a ROM in which sin and cos values are stored.
The phase difference θ _e given from the phase difference counter 17 is
The sin value and cos value are read from ROM18.

Numerals 19 and 20 are multiplication type D/A converters (digital-to-analog converters), which perform D/A conversion of the values of sin θ _e and cos θ _e read from the ROM 18 .
These converters are provided with motor torque command signals.

21 and 22 are constant current amplifiers, which are multiplication type D/
Based on the signals from the A converters 19 and 20, a constant current is passed through the coils L ₁ and L ₂ of the DD motor 23.

24 is a position detection circuit that detects the rotational position of the code plate 1. A specific configuration of this circuit is shown in FIG.

In FIG. 4, 31 is a shift register, and switches SW1 to SW8 are turned on in sequence.

32 is a timing generation circuit, which generates a signal f ₁ (t) at the timing when the 8th switch SW8 is turned on.
is applied to the take-in counter 33 and the latch circuit 34. The counter 33 counts the phase shift of the signal f ₁ (t) based on the timing of the clock generator 35. The clock generator 35 is, for example, 12MHz.
generates a clock signal. The latch circuit 34 latches the count value of the counter 33.

36 is a frequency dividing circuit which divides the frequency of the clock signal of the clock generator 35 by, for example, 1/512, and supplies it to the shift register 31 as an on/off timing signal for the switches SW1 to SW8.

A microprocessor 37 calculates the rotational position of the code plate based on the signal from the latch circuit 34.

The output signals of photodiodes D ₁ and D ₂ are amplified by an amplifier 38 and then sent to a microprocessor 37 via a buffer 39 . This signal becomes the reference position signal (zero signal).

Next, the operation of such a control device will be explained.

The scan frequency of switches SW1 to SW8 _is 8fs
is set to .

The light passing through the outer transparent slit 2 is detected by a photodiode array 8, and the light passing through the inner transparent slit 3 is detected by a photodiode array 9. When the detection signals of these photodiode arrays are scanned at a frequency of 8 f _s , the signals f ₁ (t) and f ₂ (t) that have passed through the low-pass filters 13 and 14 are as follows.

f ₁ (t) = A ₁ sin (ωt + n ₁ θ) f ₂ (t) = A ₂ sin (ωt + n ₂ θ) A ₁ , A ₂ : Constant, θ: Rotation angle of code plate ω = 2πf _sHere , The phase difference φ between both signals is φ=(n ₁ −n ₂ )θ.

Here, the relationship between the phase difference φ and the rotation angle θ of the code plate will be explained.

For example, a case will be explained in which the number of outer slits n ₁ is eight and the number of inner slits n ₂ is six.

In this case, the number m of teeth of the motor is set from 8-6 to 2.

In this case, the relationship between the detection signals of the photodiode arrays 8 and 9 and the rotation angle of the motor is as shown in FIGS. 5a and 5b.

As shown in the figure, the deviation (electrical angle) of these detection signals is proportional to the rotation angle θ (mechanical angle), and becomes φ ₁ , φ ₂ , etc.
and increases.

The deviation φ between both detection signals when the code plate is rotated by θ is given by the following equation.

φ=(8-6)θ On the other hand, when the code plate rotates by θ, the rotor of the motor also rotates by θ. Since the number of teeth of the motor is two, the teeth of the motor's rotor and stator are angularly shifted by 2θ in terms of electrical angle. That is, the phase difference detected by the code plate corresponds to the electrical angle difference between the teeth of the motor's rotor and stator. Based on this, the positional relationship (mechanical angle) between the teeth of the motor's rotor and stator is detected, and the commutation of the motor is controlled based on this positional relationship.

Next, the operation of compensating for errors due to eccentricity of the code plate will be explained.

Now, if the number of pulses according to the position of the code plate (hereinafter referred to as the number of position pulses) obtained from the signals f ₁ (t) and f ₂ (t) are N ₁ and N ₂ , then N ₁ = +δ/R ₁ sin N ₂ =+δ/R ₂ sin: true rotation angle, δ: eccentricity, R ₁ : mounting radius of photodiode array 8, R ₂ : mounting radius of photodiode array 9. From the formula, the true rotation angle is: = {A-BR ₁ -R ₂ /R ₁ +R ₂ }/2 Here, A=N ₁ +N ₂ and B=N ₁ -N ₂ .
Errors due to eccentricity are corrected by calculating using the formula.

Such error correction calculations are performed by a separately provided microprocessor.

In addition, in the embodiment, the case where the motor is a two-phase motor was explained, but the motor is not limited to this.
It may also be a phase motor. In this case, the phases of the current signals flowing through each coil are θ _e , θ _e −120°, θ _e +120°
become.

[effect] According to the present invention, the following effects can be obtained.

In other words, the number of slits is set so that the difference between the number of transparent slits on the outside and inside of the two-stage transparent slit row is the number of poles of the motor, so it is possible to use a larger number of transparent slits than the number of poles of the motor. can be provided. This improves displacement detection accuracy since the angular resolution can be reduced. Furthermore, since the pitch of the light-transmitting slits can be made small, the light source can also be made small. From Figure 6, the photodiode array
The error E caused in the detection signal due to the error Δ in the mounting radius R of the PDA is as follows: E=2π/nΔ/R n: number of slits. From the formula, the smaller n and R are, the smaller the error E is.

Furthermore, since the number of light-transmitting slits can be increased, the mounting radius of the slits can be increased. This allows a large hole to be formed in the center of the code plate.
Wiring for the motor and displacement transducer can be easily passed through.

In addition, the detection accuracy can also be improved because it is configured to compensate for errors due to eccentricity of the code plate based on the detection signals of the two photodiode arrays.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of a motor control device according to the present invention, FIG. 2 is a diagram showing the arrangement relationship between a photodiode and a light-transmitting slit, and FIGS. A diagram showing a specific configuration example of the control device, FIG. 5 is an explanatory diagram of the operation of the control device in FIG. 1,
FIG. 6 is a diagram for explaining errors occurring in the control device of FIG. 1. 1... Code plate, 2, 3... Translucent slit, 4,
5...Light source, 8, 9...Photodiode array, 10...Signal processing unit.

Claims (1)

[Claims] 1. A code plate in which transparent slits are formed at a predetermined pitch is attached to the rotor of a brushless motor,
In a motor control device that projects light onto the transparent slit and determines the positional relationship between the rotor and stator teeth of the motor based on the light passing through the transparent slit, the number of transparent slits is n on the code plate. ₁ and n ₂ two-stage slit rows are provided, n ₁ − n ₂ (n ₁ > n ₂ ) is set to the number of teeth of the motor, and the n ₁ and n ₂ transparent slits are set to the number of teeth of the motor. 1. A motor control device comprising: a signal processing unit that determines a positional deviation between teeth of a rotor and a stator of a motor from a phase difference between detection signals of passing light.